The freeze fracture procedure is being used: 1) to determine the stability of the alveolar lining layer; 2) to observe the ultrastructure of the lung from new-borns dying of hyaline membrane disease and non-respiratory diseases; 3) to mimic a routine autopsy procedure; 4) to observe changes in the ultrastructure of Type II cell secretion using the model system of pilocarpine stimulation; 5) to localize carbohydrate-lectin binding sites at the alveolar cell surface; 6) to study more general properties of the membranes of the cells in the lung such as: cell junctions, pinocytotic vesicles, and secretion granules. Biochemical and microscope radioactivity techniques are being used to study the elaboration, biosynthesis, and secretion of pulmonary surfactant. These are being done at several levels: 1) to determine the nature of the "secretion delay" and/or "storage" of lamellar body surfactant; 2) to determine losses incurred when processing lung for electron microscopy; 3) to accomplish quantitative autoradiography at the light and electron microscope levels.